Data transmission control apparatus for system with input/output units used in common by several CPU&#39;s

ABSTRACT

There is disclosed a data transmission control apparatus in which an image processing unit, for example an image input or output device, is commonly used for plural central processing units for improving the efficiency of the system. A control unit selectively converts one or another of the CPU&#39;s to the desired image processing unit, monitoring the status of the connection(s) and refusing new requests for connection to that image processing unit until the latter is no longer needed by the CPU connected to it.

This application is a continuation, of application Ser. No. 07/972,738filed Nov. 6, 1992, which is a continuation of application Ser. No.07/524,711, filed May 21, 1990, which is a continuation of applicationSer. No. 07/022,016, filed Mar. 5, 1987, all now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a data control apparatus, and moreparticularly to a data transmission control apparatus in whichinput/output units are commonly used by plural central processing units.

2. Related Background Art

In conventional systems, for example image processing systems, eachcentral processing unit (CPU) is often equipped with at least an imageinput unit such as an image reader or an image output unit such as animage printer. However, in such a system, the proportion of use of suchimage input/output units is quite low compared to the entire processingtime of the system, and the connection of an expensive imageinput/output unit to each CPU is very inefficient. For this reason therehas been proposed a system which is provided with a printer controlunit, called a printer server, by means of which a printer unit iscommonly utilized by plural CPU's through a local area network (LAN).However, such a system involves complicated LAN and common control andis not suitable for a small system.

SUMMARY OF THE INVENTION

In consideration of the foregoing an object of the present invention isto provide a data transmission control apparatus in which a dataprocessing unit can be commonly utilized by plural central processingunits and can therefore be utilized effectively.

Another object of the present invention is to provide a datatransmission control apparatus in which a data processing unit connectedto central processing units can be utilized not only in relation to saidcentral processing units but also independently.

The foregoing and still other objects of the present invention, as wellas the features and advantages thereof, will become fully apparent fromthe following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a common control unit embodying the presentinvention;

FIG. 2 is a circuiting diagram showing the connection of the commoncontrol unit of the emodiment of FIG.1;

FIG. 3 is a flow chart showing the receiving operation of a controlunit; and

FIG. 4 is an explanatory chart showing various states of the commoncontrol unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Now the present invention will be clarified in detail by description ofthe embodiment shown in the attached drawings.

FIG. 1 is a block diagram showing an embodiment of the presentinvention, wherein central processing units (CPU) 1, 2 commonly have animage reader 4 and an image printer 5 through a common control unit 3.Said CPU's 1, 2 are information processing units such as work stations,personal computers or word processors. The image reader 4 enters thelight reflected from an original image through optical means, into aphotoelectric converting element such as a CCD image sensor, andconverts the entered light by said photoelectric converting element intoimage data consisting of serial electric signals representing thedensity of pixels.

The image printer 5 receives the image data consisting of serialelectric signals and reproduces the image, in the form of a dot image,on a sheet. Said image printer can be composed, for example, of aso-called laser beam printer, in which a laser beam modulated accordingto the image data scans a photosensitive drum to form a latent imagecorresponding to said data, and said latent image is then developed andtransferred to reproduce the image on a sheet, an electrostatic printerprovided with electrostatic electrodes, an ink jet printer achieving aprinting operation by the emission of ink droplets, or a thermal printerfor image printing by thermal color development, including a thermaltransfer printer.

The image reader 4 may be directly linked with the image printer 5 tofunction as a copying machine.

In response to a connection request from the CPU 1 or 2 (i.e., a requestto be converted to an input and/or to an output device), the commoncontrol unit 3 connects the CPU with the image reader 4 or the imageprinter 5. Also when none of the CPU's 1, 2 is connected to the imagereader 4 or the image printer 5, the image reader 4 is automaticallyconnected to the image printer 5 to function as a copying machine.

FIG. 2 is a block diagram showing the structure of the common controlunit 3.

A connection switch circuit 11 switches the connection between the imagereader 4, image printer 5 and the CPU's 1, 2 according to a switchingsignal 16 from a control unit 10. Parts of interface signals of theimage reader 4 and the image printer 5 are supplied as status signals tocontrol unit 10 through signal lines 14, 15, and said control unit 10inspects the function status of the image reader 4 and the image printer5 through said status signals.

The control unit 10, for controlling the common control unit 3 inresponse to said status signals and interface signals 17, 18, isprovided with a microprocessor (MPU) 100, a ROM 101 storing controlprograms and data therefor, and a RAM 102 serving as a working area.

The control signals 17, 18, supplied to the control unit 10 for commoncontrol respectively from the CPU 1 and CPU 2, are transmitted in theform of serial data. There are also shown image reader interface signals19, 21 respectively of the CPU 1 and CPU 2, and image printer interfacesignals 20, 22 respectively of the CPU 1 and CPU 2. Switches 12, 13 inthe connection switch circuit 11 are mutually linked and select thecontacts A, B or C in response to the switch signal 16 from the controlunit 10, thus controlling the connection between the CPU's and the imagereader 4 and image printer 5. Said switches 12, 13 are composed of logiccircuits.

The image reader interface signal 23 and the image printer interfacesignal 24 are composed of communication signals for exchanging commandsand status messages and image signals for entering or releasing imagedata, and the direction of input or output of the image signals ismutually inverse between the image reader interface signal 23 and theimage printer interface signal 24.

In the function as a copying machine, the image reader 4 assumes a modeof directly controlling the image printer 5, called an off-line mode. Inthis state the switches 12, 13 are switched to the contacts C inresponse to the switch signal 16 from the control unit 10, whereby theimage reader interface signal 23 and the image printer interface signal24 are exchanged between the image reader 4 and the image printer 5,through a signal line 25.

If a copy start key of the image reader 4 is actuated for example in theoff-line mode, the image reader 4 starts image reading and supplies theimage printer 5 with image data for executing a printing operation,whereby a copying operation as a copying machine is achieved.

On the other hand, when connected to either of the CPU1 and CPU2, theimage reader 4 and the image printer 5 function in a slave mode toachieve a reading operation or a printing operation under the control ofthe CPU 1 or CPU2. This mode is called an on-line mode.

The on-line mode or the off-line mode in the image reader 4 can beselected by an on-line command or an off-line command supplied thereto,in the form of communication signals of the image reader interfacesignal 23, from the control unit 10 through the signal line 14.

The interface signals 17, 18 are the well known serial interfacesignals, called RS232C, by means of which the control unit 10 exchangescommands and status messages for common control with the CPU's 1 and 2.When the CPU 1 wishes to use the image printer 5, it checks the statusof the common control unit 3 through the interface signal 17, and, ifthe image printer 5 is available, it releases an open command to requestexclusive use of the image printer 5 by the CPU 1. When the exclusiveuse state is established by the reception of said open command, the CPU1 performs a printing operation with the image printer 5, and, after thecompletion of said printing operation, it releases a close command todeclare the end of such exclusive state, thereby terminating the controlsequence.

The switching of the connection switch circuit 11 by the control unit 10is prohibited in certain states of the image reader 4 and the imageprinter 5. Such prohibition takes places firstly when the image reader 4or the image printer 5 is exclusively used by the CPU1 or CPU2, namelyin a period from the reception of an open command to the reception of aclose command from the CPU, and secondly in the off-line mode, or in alocal copying mode, in which the image reader 4 and the image printer 5function as a copying machine though neither is exclusively used byeither CPU. For this purpose the control unit 10 has to detect a copyingoperation in progress, by monitoring the communication signals of theimage reader interface signal 23, thereby inspecting the communicationbetween the image reader 4 and the image printer 5.

The copying sequence is conducted in the following manner. A copypreparation stage consists of rotating a photosensitive drum of theimage printer 5, and supplying a recording sheet to a predeterminedposition from a cassette when said drum reaches a predeterminedrevolution.

Then the copying operation is conducted by synchronizing the readingoperation of the image reader 4 with the printing operation of the imageprinter 5. After the sheet with a copied image is discharged, the imageprinter 5 terminates the rotation of the photosensitive drum, and checksfor the presence of any abnormalities such as sheet jamming, therebycompleting the copying sequence. Thus the control unit 10 monitors thecommunication between the image reader 4 and the image printer 5, anddetermines a switching prohibition period by detecting the period from acommand for starting the rotation of the photosensitive drum to an endstatus signal following a command for stopping the rotation of saiddrum.

In the communication signals of the image reader interface signal 23 andthe image printer interface signal 24, each command is always respondedto by a status signal from the recipient of the command signal. Thus theswitching is naturally prohibited in a period from the sending of thecommand signal to the return of the status signal.

FIG. 3 is a flow chart of a sequence, stored in the ROM 101 of thecontrol unit 10 of the common control unit 3, for receiving signals fromthe CPU of the MPU 100.

At first, if a step S1 discriminates the reception of an open command,requesting the exclusive use of the image reader 4 or the image printer5, from the CPU1 or the CPU2, the program proceeds to a step S2 forinspecting the state of use of other CPU's. In the following there willbe explained the function of the MPU 100, in a case where an opencommand is received from the CPU1. In response to an open command fromthe CPU1, and, if the CPU2 is not in use, the program proceeds to a stepS3 for inspecting whether the image reader 4 and the image printer 5 arein a copying operation in the off-line mode. If a copying operation isin progress, or if the step S2 identifies that the CPU 2 is occupied,the program proceeds to a step S4 to send an unavailable-for-receivingmessage to the CPU1.

In the so-called off-line mode in which no CPU is in use, and no copyingoperation is in progress, so that the image reader and the image printer5 are available, a step S5 sends an on-line command to the image reader4 to shift the mode to the on-line mode.

A step S6 releases a switch signal 16 to shift the switches 12, 13 tothe contacts A, in order to connect the CPU 1 with the image reader 4and the image printer 5, and a step S7 sends a status signal indicatingthe exclusive use to the CPU 1, whereby a state of exclusive use by theCPU 1 is established.

A step S8 discriminates whether a close command, indicating the end ofthe exclusive use, has been received from the CPU 1, and if it has beenreceived, the program proceeds to a step S9 to shift the switches 12, 13to contacts C by the switching signal 16. A step S10 sends an off-linecommand to the image reader 4, thus shifting the same from the on-linemode to the off-line mode, thus realizing a stand-by state.

FIG. 4 is an explanatory chart indicating the change of state of theimage reader 4, image printer 5 and common control unit 3.

After the start of power supply, a predetermined initialization isconducted in a state 40, and there is then assumed an off-line stand-bystate 41. Then, in response to an open command from the CPU 1 or CPU 2,requesting exclusive use, an on-line command is sent to the image reader4 whereby an on-line mode 42 is assumed. Then, in response to an opencommand from the CPU 1 or CPU 2, a state 43 of exclusive use by the CPU1 or a state 44 of exclusive use by the CPU 2 is assumed.

Then, in response to a close command from the CPU 1 or CPU 2, theapparatus shifts from said state of exclusive use by the CPU 1 or CPU 2to the on-line stand-by state 42, and it then moves to the off-linestand-by state 41 by the automatic sending of an off-line command to theimage reader 4.

If an unrepresented copy start key of the image reader 4 is depressed bythe operator during the off-line stand-by state, the apparatus shifts toa local copy mode 45 for a copying operation. After the completion ofthe copying operation, the off-line stand-by state 41 is assumed again.

In the present embodiment the number of CPU's is not limited to two butcan be varied arbitrarily.

The serial interface signal for common control is not limited to theformat RS232C but can be replaced by another serial interface signal ora parallel interface signal.

Also the connection switch circuit 11 switches the image readerinterface signal and the image printer interface signal simultaneouslyto a same CPU, but it may switch said signals to different CPU's atdifferent timings.

In this manner the present invention can be modified in various mannerswithin the scope and spirit thereof.

In the foregoing explanation the input and output units are explained asan image reader and an image printer, but they are not limited to suchexamples and can for example be other input/output units such as animage file capable of accumulating a large amount of image information,a communication unit to be connected to a communication line fortransmission of information, or a display unit for displaying an imageaccording to image information. Also the number of such input/outputunits can be arbitrarily increased or decreased.

As explained in the foregoing, the present embodiment allows pluralcentral processing units to commonly use image input/output unitswithout modifying the interface signal thereof.

Also, when not connected to the central processing units, the imageinput and output units can be mutually connected to achieve a functionas a copying machine, thereby enabling effective utilization of suchunits.

The present invention is not limited to the foregoing embodiments but issubject to various modifications and variations within the scope andspirit of the appended claims.

I claim:
 1. An image data transmission control apparatus for controllinga data transmission among a plurality of data processing apparatuses, areader which reads an image to supply image data to the data processingapparatuses and a printer which prints an image in accordance with imagedata from the data processing apparatuses, comprising:switch means forconnecting any one of the data processing apparatuses to the reader orthe printer, so as to transmit image data between a connected dataprocessing apparatus and the reader or the printer and for connectingthe reader to the printer, so as to print an image by the printer inaccordance with image data from the reader; and control means forcontrolling said switch means in response to an open command forrequesting use of the reader or the printer and a close command fordeclaring end of use of the reader or the printer, which commands aresent from the data processing apparatuses, so that said switch meansconnects the reader and the printer during a stand-by period, andconnects a one of the data processing apparatuses to the reader or theprinter when the open command is sent from the one of the dataprocessing apparatuses, and disconnects the one of the data processingapparatuses from the reader or the printer and connects the reader tothe printer when the close command is sent from the one of the dataprocessing apparatuses; wherein, after the one of the data processingapparatuses is connected to the reader or the printer, said controlmeans inhibits a changeover of the connection made by said switch meansto another data processing apparatus until the close command is sentfrom the one of the data processing apparatuses, even if another opencommand is sent from the another data processing apparatus, wherein saidcontrol means inhibits a changeover of the connection made by saidswitch means to any of the data processing apparatuses while the printeris printing an image in accordance with image data from the reader, evenif the open command is sent from any of the data processing apparatuses,and wherein said control means includes sending means for sendinginformation representing unavailable-to-receive to one of the dataprocessing apparatus, and said sending means sends the informationrepresenting the unavailable-to-receive to the data processing apparatuswhich has sent the open command during a time said control meansinhibits a changeover of the connection made by said switch means.
 2. Anapparatus according to claim 1, wherein, in a case where said controlmeans makes said switch means changeover in response to an open commandfrom a data processing apparatus, said control means issues a messagerepresentative of acceptance of the open command to the data processingapparatus which has sent the open command.
 3. An apparatus according toclaim 1, wherein, before the data processing apparatus, which sent theopen command, sends the close command, if another data processingapparatus sends another open command, said control means issues amessage representative of refusal of the another open command to theanother data processing apparatus.
 4. An apparatus according to claim 1,wherein the data processing apparatuses are a work station, a personalcomputer or a word processor.
 5. An image data transmission system,comprising:a plurality of data processing apparatuses for processingimage data; a reader for reading an image to supply image data to saiddata processing apparatuses; a printer for printing an image inaccordance with image data from the data processing apparatuses; switchmeans for connecting any one of said data processing apparatuses to saidreader or said printer, so as to transmit image data between a connecteddata processing apparatus and said reader or said printer and connectingsaid reader to said printer, so as to print an image by said printer inaccordance with image data from said reader; and control means forcontrolling said switch means in response to an open command forrequesting use of said reader or said printer and a close command fordeclaring end of use of said reader or said printer, which commands aresent from said data processing apparatuses, so that said switch meansconnects said reader and said printer during a stand-by period, andconnects a one of said data processing apparatuses to said reader orsaid printer when the open command is sent from the one of said dataprocessing apparatuses, and disconnects the one of said data processingapparatuses from said reader or said printer and connects said reader tosaid printer when the close command is sent from the one of said dataprocessing apparatuses; wherein, after the one of said data processingapparatuses is connected to said reader or said printer, said controlmeans inhibits a changeover of the connection made by said switch meansto another data processing apparatus until the close command is sentfrom the one of said data processing apparatuses, even if another opencommand is sent from the another data processing apparatus, wherein saidcontrol means inhibits a changeover of the connection made by saidswitch means to any of said data processing apparatuses while saidprinter is printing an image in accordance with image data from saidreader, even if the open command is sent from any of said dataprocessing apparatuses, wherein said control means includes sendingmeans for sending information representing unavailable-to-receive to oneof said data processing apparatuses, and said sending means sends theinformation representing the unavailable-to-receive to said dataprocessing apparatus which has sent the open command during a time saidcontrol means inhibits a changeover of the connection made by saidswitch means.
 6. A system according to claim 5, wherein, in a case wheresaid control means makes said switch means changeover in response to anopen command from a data processing apparatus, said control means issuesa message representative of acceptance of the open command to the one ofsaid data processing apparatus which has sent the open command.
 7. Asystem according to claim 5, wherein, before the data processingapparatus, which sent the open command, sends the close command, ifanother data processing apparatus sends another open command, saidcontrol means issues a message representative of refusal of the anotheropen command to the another data processing apparatus.
 8. A systemaccording to claim 5, wherein said data processing apparatuses are awork station, a personal computer or a word processor.
 9. A datacommunication control apparatus for controlling a data communicationamong at least one data processing apparatus, a reader which reads animage and outputs image data and a printer which prints an image inaccordance with input image data, comprising:connection control meansfor controlling a connection among the data processing apparatus, thereader and the printer; detection means for detecting a connectionrequest from the data processing apparatus; discrimination means fordiscriminating whether or not the reader and the printer are incommunication; and sending means for sending predetermined informationto the data processing apparatus, wherein said connection control meanscontrols such that the reader and the printer are connected for acopying operation during a stand-by period, wherein, in a case wheresaid detection means detects the connection request from the dataprocessing apparatus, said connection control means controls such thatthe data processing apparatus and the reader or the printer areconnected to each other if said discrimination means discriminates thatthe reader and the printer are not in communication, and wherein, in thecase where said detection means detects the connection request from thedata processing apparatus, said sending means sends informationrepresenting unavailable-to-receive to the data processing apparatus ifsaid discrimination means discriminates that the reader and the printerare in communication.
 10. An apparatus according to claim 9, wherein thedata processing apparatus is a work station, a personal computer or aword processor.
 11. An apparatus according to claim 9, furthercomprising connection releasing detection means for detecting aconnection releasing request from the data processing apparatus,andwherein said connection control means controls such that the readerand the printer are connected to each other, until both the connectionrequest from the data processing apparatus is detected and after theconnection releasing requesting is detected.
 12. A data communicationcontrolling method for controlling a data communication among at leastone data processing apparatus, a reader which reads an image and outputsimage data and a printer which prints an image in accordance with inputimage data, comprising the steps of:detecting a connection request fromthe data processing apparatus; discriminating whether or not the readerand the printer are in communication; and connecting, in case ofdetecting the connection request, the data processing apparatus and thereader or the printer to each other if it is discriminated that thereader and the printer are not in communication; sending, in case ofdetecting the connection request, information representingunavailable-to-receive to the data processing apparatus if it isdiscriminated that the reader and the printer are in communication; andcontrolling a connection between the reader and the printer so that thereader and the printer are connected for a copying operation during astand-by period.